Various artificial ultraviolet radiation sources have been used in industrial and medical applications. The output of such radiation sources is well characterized in terms of the power and spectra and is fairly constant through the life time of the source. In contrast, solar radiation reaching Earth consists of electromagnetic waves across the spectrum from ultraviolet (UV) through visible light, to infrared (IR). The UV radiation (UVR) is further subdivided. UV-C, from about 200 to 285 nanometers in wavelength, is totally absorbed in the atmosphere before reaching Earth. UV-B, from about 285 to 318 nanometers, contains only a few percent of the total solar ultraviolet light energy generated, and is considered the cause of skin cancer in humans. UV-A, from about 315 to 400 nanometers, is mostly responsible for tanning; but it plays some role in skin cancer and is also the cause of eye cataracts, solar retinitis and corneal dystrophies. In addition, the interaction between UV-B and UV-A radiation is suspected to have a synergistic skin cancer causing effect Moreover, this combined ultra-violet radiation is a cause for skin aging and wrinkling.
The medical profession appears to have well documented such biological effects. However, because of the variability between individuals, exposure levels which may cause significant damage to one person may be benign to another. Further, a safe exposure level in terms of skin cancer may nevertheless cause eye damage or effect skin aging. For those who choose to seek exposure to obtain skin tanning for cosmetic purposes without most of the other negatives, despite published medical warnings to refrain from such an activity, it is helpful if such persons may regulate the amount of exposure with more quantitative and qualitative means other than simply through guessing Of prime importance is the cumulative power on the sensitive area, the energy received.
The general principles and techniques for radiometry, photometry and spectroradiometry have long been known and are adequately described in the technical literature. Based on such principles many ultraviolet radiation measuring and alarm instruments have been developed and have been available commercially for many years and others appear in the patent literature. Some use radiation-sensitive photo-chromic chemicals, others use UV-induced fluorescent properties of material, and yet others use photoconductive or photovoltaic cells. These may be considered briefly.
A reusable radiation monitor based on photochromic chemicals, described in U.S. Pat. No. 4,130,760 to Fanselow and a similar one-time monitor marketed by Lucas Products of Toledo Ohio contains a display that changes color when a predetermined cumulative energy threshold is exceeded. The monitor does not, however, display a quantitative value for the radiation. An electrochemical integration scheme, described in U.S. Pat. No. 4,372,680 to Adams et al, uses two photocells in a differential mode in order to obtain a cumulative readout of Ultraviolet Radiation. This device likewise does not display quantitative value of the radiation. In addition it requires a separate readout device for determination of the electrochemical cell status. Thus such devices appear unsuitable for applications in which the real-time radiation intensity and energy level readings are of interest as in the case of the present invention. Further, such devices cannot be used to determine the direction of maximum radiation and such determination must be made intuitively.
Another UV dosimeter presented in U.S. Pat. No. 4,403,286 to Presby, utilizes the fluorescence induced in the core of optical fibers which is then monitored by a visible light detector. Yet another meter, the "Robertson-Berger" or R-B meter, simulates the human skin response to Ultraviolet Radiation, and uses phosphor excitation by the UV-B radiation band and a visible light detector. This meter, described in "A Climatology of Sunburning Ultraviolet Radiation," by D. Berger and F. Orbach, (Photochem. & Photobiol. Vol. 35, pp. 187-192, 1982), also provides a cumulative dosage reading in peculiar units which cannot be easily transformed to the common energy units.
The need for a useful personal dosimeter as would provide assistance to those who wish to protect their skin or eyes is amply recognized in the patent literature. Thus U.S. Pat. No. 3,710,115 granted Jan. 9, 1973 to Jubb for a Sunburn Warning Device teaches a combination for providing an alarm upon attainment of a predetermined dosage or energy level received at the radiation sensor, doing so by integration of the sensor signal. Concurrently an analogue meter provides continuous display of the dosage level attained.
U.S. Pat. No. 3,878,496 granted Apr. 15, 1975 to Erickson for a Selectable Level Alarming Personal Dosimeter presents a personal radiation dosimeter, that warns of excessive radiation dosage, in this case atomic radiation, and also alerts the user if there is a rapid increase in level as would likely rapidly lead to the dosage limit. Erickson's device incorporates the technique of electronic counting as the means to determine dosage, as an alternative to direct electronic integration.
A similar approach is described in U.S. Pat. No. 3,917,948 granted Nov. 4, 1975 to Strutz for a UV dosage monitoring and alarm device combination. In the radiometer circuits a signal is generated whose pulse repetition rate is proportional to the intensity of UV radiation detected by the sensor; and the circuit electronically counts such pulses and uses the count as a representation of accumulated energy.
Further, U.S. Pat. No. 4,535,244, granted Aug. 13, 1985 to Burnham discloses a portable dosimeter that contains a sensor, a microprocessor and a display, wherein an alarm may be given upon attainment of a preselected dosage. A keyboard is included to allow selection of the desired dosage level. Another selection allows user adjustment to take into account the use of sunscreen material, the SPF factor. Electronic circuits divide the accumulated dosage by a factor that corresponds to the solar protection factor value entered by the user via the keyboard.
Burnham's dosimeter is improved upon as described in U.S. Pat. No. 4,608,492, granted Aug. 26, 1986 to Burnham by adding to a personal UV dosimeter combination a circuit for advising the user if the UV sensor is obscured by the user or malfunctions. Thus, if sequential readings of the sensor differ substantially from one moment to the next, which represents either failure of the pickup cell or an inadvertent movement by the user obscuring or covering the radiation sensor, an alarm condition is signalled.
U.S. Pat. No. 4,704,535, granted Nov. 3, 1987 to Lieber, et al presents construction details for a novel UV sensor intended for use in a portable UV dosimeter. A specific filter blocks the Infrared radiation from reaching the photocell.
U.S. Pat. No. 4,229,733 granted Oct. 21, 1980 to Tulenko et al for an Exposure Detecting Device discloses another personal UV alarm combination, one with an added feature that automatically adjusts for "recovery". Thus even though the accumulated dosage is of a certain level, if one leaves the sun and commences recovery, the circuit simulates that action and subtracts prescribed amounts from the stored accumulated levels; commencing again when the unit is again subjected to the radiation.
With the foregoing background in the patent literature, one may consider an aspect of solar radiation that the identified patents overlook. Global ultraviolet radiation exposure is composed of direct solar radiation; that is, radiation traveling in-line with the sun, and indirect radiation, that is radiation scattered and reflected from all other angles, and that combination is strongly affected by several factors. Environmental conditions, such as clouds, humidity, haze and fog, seasonal local and global variations in the ozone layer, all contribute to the scattering and blocking to a various degree of the direct ultraviolet radiation. Geographic parameters such as latitude, altitude, and solar zenith angle, determine the path length through the atmosphere and the resulting attenuation of the direct radiation. A portion of the scattered ultraviolet radiation due to these effects also reaches Earth at oblique angles. The ambient surroundings such as surface type (water, snow, sand, concrete, glass, etc) and the topography determine the reflection of ultraviolet radiation. A part of this reflected ultraviolet radiation is again scattered in the atmosphere and returned to Earth. Such complex interplay affects the total radiation exposure to which a person is subjected. Thus it may be appreciated that not only is it impractical to predict the direction and amount of maximum total radiation but it is also difficult as to how to measure. For example one may recall the well known fact that a person sitting on the beach under a parasol may still incur a severe sunburn due to the ultraviolet radiation reflected from the sand and water.
In order to obtain the best assessment of exposure to ultraviolet radiation, there thus exists a need to determine the direction from which the maximum radiation arrives and then to point the radiometer in that direction. Though personal dosimeters are extensively considered in the described patent literature, those patents and the disclosed technology fail to appreciate a need for the sunbather or other person who is trying to avoid exposure, such as the beach enthusiast who sits under a parasol, to orient the dosimeter in the direction of maximum power and therefor fail to include appropriate means for enabling the user to make that determination. Guessing is clearly unreliable.
The failure of the patent literature to recognize this need is also reflected in the available instrumentation for industrial or commercial use. Electronic apparatuses for measuring radiation power are not new. For example, one such power measuring instrument has been available for many years from the Solar Light Co. of Philadelphia Pa. Using that instrument it is possible to locate the direction of maximum radiation power in application addressed in this application given the teaching and using the method herein described. Thus given the present teaching one might employ available commercial instruments, based on the said R-B meter, which measures radiation intensity, instantaneous power of Ultraviolet Radiation in relative units, although not in absolute units of power, and use the R-B meter together with one of the personal dosimeter devices shown in the patents earlier described or with one of the other kinds of commercial instruments that measures dosage in relative units.
Commercial industrial instruments of the foregoing type operate either as a power meter or an energy meter, but none performs both functions. Most are large in size, heavy, require electricity to operate and thus are believed to be impractical for use as a personal portable device. Indeed because of the large size of those commercial units, the sensor unit is in many cases attached with an electrical cord to the measuring unit so that the sensor may easily be moved around and positioned. The foregoing commercial instruments alone or in combination do not appear to serve as a portable self contained radiometer that may be used by sunbathers to monitor ultraviolet radiation energy and power.
Accordingly, an object of this invention is to provide an improved personal miniaturized radiometer for ultraviolet radiation detection and measurement that allows the user to keep record of cumulative exposure over prolonged periods of time.
A further object of the invention is to provide an easy to use inexpensive portable radiation dosimeter that provides an effective dosage alarm as should warn of impending overexposure to any portion of the user's body.
A still further object of the invention is to provide a relatively inexpensive and compact radiation dosimeter structure using readily available technology and capable of manufacture by mass production techniques.
An ancillary object of the invention is to provide a personal dosimeter that may be carried by the person and has wide versatility, permitting the user to set the mode of display in absolute units or in terms of percentage or relative units as desired for any particular application.